The present invention relates to a device for detecting adhesion in relays due to melting for use in electrically driven vehicles, such as electric motor vehicles, wherein the relay is interposed between a load circuit including an electric motor and a plurality of batteries for effecting or interrupting the supply of current from the batteries to the load circuit.
Electric motor vehicles are provided with a power source unit having a high voltage and a great capacity and comprising a plurality of secondary batteries, such as lead batteries or nickel hydrogen batteries, which are connected in series. Electric power is supplied from the power source unit to a load circuit including an electric motor.
Provided between the power source unit and the load circuit is a main relay, which is energized or deenergized by an on/off manipulation of a key switch (ignition switch) of the electric motor vehicle.
When the key switch is turned off by the user, the main relay is deenergized to electrically separate the load circuit from the power source unit, thereby preventing useless consumption of power and ensuring safety of maintenance.
The current flowing through the main relay and the load circuit is as great as up to 400 A if maximum, whereas the main relay capable of blocking the passage of such a great current is large-sized and expensive, so that main relays in used are smaller than 400 A in the value of the current that can be blocked.
When the main relay is erroneously deenergized in a state wherein the electric motor vehicle is accelerated, for example, for starting, with a great current flowing through the main relay, it is likely that the main relay fails to completely block the passage of current instantaneously, permitting occurrence of an arc across the contacts of the relay and adhesion of the contacts by melting.
Further when the electric motor vehicle is rapidly accelerated or decelerated during driving, a great charge or discharge current will flow through the main relay, consequently causing adhesion of the main relay contacts on melting.
If the main relay contacts become thermally adhered as described above, an abnormal current flows through the load circuit to cause damage to the electric motor or like load. The main relay is then unable to reliably prevent the power source unit from wasting electric power and to ensure the safety of maintenance.
Accordingly, a device has been proposed for detecting adhesion in main relays of electric motor vehicles due to melting by checking the presence or absence of current through a closed loop circuit which includes the main relay and a plurality of secondary batteries for providing a power source for the electric motor, etc. (JP-A No. 2000-173428)
However, the secondary batteries provided on the electric motor vehicle as the power source for the motor, etc. are all used as the power source for the main relay adhesion detecting device for the vehicle, so that a high voltage is applied to the main body of the device. This entails a need to use elements of great voltage resistance in constructing the circuit, further giving rise to the problem of making the device body greater in size and also the problem of low safety.
An object of the present invention is to provide a device having a compact main body and ensuring high safety for detecting adhesion in relays due to melting.
In an electrically driven vehicle wherein a relay is provided between a load circuit including an electric motor and a plurality of batteries for effecting or interrupting the supply of current from the batteries to the load circuit, the present invention provides a relay adhesion detecting device for detecting occurrence or absence of adhesion in the relay due to melting by detecting presence or absence of current flowing through the relay when the relay is unenergized using one or more of the batteries as a power source.
When the contact of the relay is not adhered by melting with the relay unenergized, no current flows through the relay and current flowing through the relay is not produced, but if the relay contact is adhered by melting, the current from one or more of the plurality of batteries flows through the relay to pass through the relay.
With the relay adhesion detecting device of the invention, accordingly, the relay is checked for the adhesion of its contact due to melting by detecting the presence or absence of current flowing through the relay.
The relay adhesion detecting device embodying the invention utilizes as its power source one or more of the plurality of batteries provided in the electrically driven vehicle and serving as a power source for the load circuit including the electric motor, so that the voltage to be applied to the device main body is lower than in the case of the conventional relay adhesion detecting device for which all the batteries installed in the vehicle serve as the power source. This makes it possible to use elements of small voltage resistance for the circuit, to compact the device main body and to achieve improved safety.
Stated more specifically, the device comprises:
a current passage line for passing current through the relay from one or more of the batteries serving as the power source,
line switching means provided on the current passage line for opening or closing the current passage line, and
adhesion detecting means provided on the current passage line for detecting occurrence or absence of adhesion in the relay due to melting by detecting presence or absence of current flowing through the current passage line.
When the relay contact is free of adhesion and opened with the line switching means closed in this specific construction, no current flows through the current passage line, whereas if the relay contact is adhered by melting, current flows through the line as closed.
With the specific construction, therefore, the relay can be checked for the adhesion of its contact due to melting by detecting the presence or absence of current flowing through the current passage line.
If the construction used has no line switching means and when the relay contact is adhered by melting, current would flow through the line over a long period of time to result in a waste of electric power.
With the specific construction described, on the other hand, the line switching means is closed only when the relay is checked for adhesion, obviating useless consumption of power.
Further stated specifically, the line switching means comprises:
a photocoupler provided on the current passage line and operable by being supplied with current, and
current supply means for supplying actuating drive current to the photocoupler.
When actuating drive current is supplied to the photocoupler from the current supply means in this construction, the photocoupler is actuated with the current to close the current passage line. If the supply of current to the photocoupler from the supply means is interrupted, on the other hand, the photocoupler is brought out of conduction upon detecting the interruption to open the current passage line. In this way, the line is closed or opened in accordance with the supply of current from the supply means to the photocoupler or interruption of the supply.
Further stated specifically, the adhesion detecting means comprises:
a photocoupler provided on the current passage line and operable by being supplied with current, and
means for checking the relay for adhesion due to melting based on the on/off state of the photocoupler.
When the relay is free of adhesion due to melting, no current flows through the current passage line in this specific construction as stated above, so that the photocoupler is then out of conduction. In the event of adhesion in the relay, current flows through the line to bring the photocoupler into conduction.
Accordingly, the relay is found free of adhesion when the photocoupler is off, whereas when in conduction, the photocoupler indicates adhesion occurring in the relay.
Further stated specifically, the current passage line is provided with a resistor for limiting the magnitude of current to be passed through the current passage line to not greater than a predetermined value.
In this specific construction, the magnitude of the current to be passed through the current passage line is limited to not greater than the predetermined value by the resistor. The above-mentioned one or more of the batteries can therefore be prevented from becoming thermally damaged owing to an excess current.
Stated further specifically, the device comprises means for informing the user of adhesion occurring in the relay due to melting when the adhesion is detected.
In the event of adhesion occurring in the relay due to melting in the specific construction, the user is informed of the occurrence of adhesion in the relay by a known method or information, for example, by actuating an alarm buzzer or turning on an alarm lamp. Accordingly, the person possessing or maintaining the vehicle can be readily informed of the thermal adhesion in the relay.
As described above, the relay adhesion detecting device embodying the invention for use in electrically driven vehicles can be compacted in the device main body and improved in safety.